A White House spokeswoman Tuesday night said U.S. intelligence officials are “working as quickly as possible” to determine the authenticity of a video in which Islamic militants claim to have beheaded an American journalist in retaliation for airstrikes in Iraq.

“If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends. We will provide more information when it is available,” National Security Council spokesman Caitlin Hayden said in a statement.

A video released online claims to show the execution of James Foley, an American photojournalist who went missing while covering Syria’s civil war.

As the video plays out, a masked executioner threatens a second prisoner, identified as Steven Joel Sotloff, also a journalist who disappeared in Syria.

“The life of this American citizens, Obama, depends on your next decision,” the militant says.

Foley was working as a photographer in Syria for the Boston-based news website GlobalPost when he went missing in November 2012. He previously worked as a reporter for Stars and Stripes. Sotloff, a freelancer who reportedly worked for Time, the National Interest and Media Line, disappeared in Syria in August 2013.